Currents in Submarine Canyons: An Air-Sea-Land Interaction

Abstract

x8090 Submarine canyons serve as active conduits joining the shallow waters of the shelf to the deeper waters offshore. Canyon currents are generated by many forces, including those related to wind, surface waves, internal waves, tides, and suspended sediment. Studies of canyon currents indicate that submarine canyons can generally be divided into deep- and shallow-water regimes that are dominated by specific driving forces. The deep-water regime is generally exposed to energy from tides, intern al waves, and spin-off eddies from large-scale current systems, whereas the shallow-water areas are dominated by currents related to surface waves and wind. Strong down-canyon currents appear to be caused by a unique combination of air-sea-Iand interactions consisting of 1. a pile-up of water along the shoreline caused by strong onshore winds; 2. down-canyon pulses of water associated with groups of high incident waves; 3. excitation of standing edge waves that produce longer-period up-and down-canyon oscillations; and finally, 4. the formation of discrete pulses of down-canyon motion, which become more intense and lead to sustained down-canyon currents, as the weight of the sediment suspended by the currents overcomes the density stratification of the deeper water. Simultaneous measurements of currents and pressure in Scripps Submarine Canyon, and of winds, waves, and pressure over the adjacent shelf have been made for several years, with the strongest down-canyon current measured, 1.9 m sec-1 at a depth of 44 m, being recorded during the